1. Field of the Invention
The present invention generally relates to electronic devices, and in particular, relates to circuitry that provides dynamic termination for a bus, such as those in open-drain bus architecture systems.
2. Background Information
Operating frequencies of processors are progressively increasing. In order to take advantage of these high frequencies, computer systems attempt to transmit signals along their buses and between system components at comparable frequencies.
When transmitting and receiving data at high frequencies between system components, such as between semiconductor components, some problems are encountered. Buses behave like transmission lines, where impedance mismatches lead to signal reflection and interference effects, such as ring-backs and overshoots. Maintaining signal quality over interconnections thus typically require termination of the transmission lines (e.g., buses) with matching impedances to minimize signal reflections.
With what is sometimes referred to as xe2x80x9cdual-ended termination,xe2x80x9d transmission lines used to carry signals in both directions are terminated at both ends (e.g., at agents at each end), such that a terminating resistor matches a characteristic impedance of the transmission line. However, having the termination resistor at the driving end of the transmission line needlessly dissipates power, particularly when a low voltage level (e.g., a binary 0) is driven onto the transmission line, since a current flows through the termination resistor at that driving end. Attempts to avoid this power dissipation include system architectures that provide a termination resistor on only one side of the transmission line (sometimes referred to as xe2x80x9csingle-ended terminationxe2x80x9d ), but such single-ended termination architectures result in a positive reflection coefficient at the un-terminated end of the transmission line, which is an adverse result for a high-performance and high-frequency bus.